1. Field of the Invention
The present invention relates to a method of producing a laminated electronic component and, more particularly, to a method of producing a laminated electronic component such as a laminated inductor or other suitable device in which ceramic green sheet layers and electro-conductor layers made from conductive paste are laminated to each other and are fired to produce a ceramic sintered body.
2. Description of the Related Art
Ordinarily, in production of laminated ceramic electronic components, an electro-conductive paste for formation of internal electrodes is screen-printed to form a conductive pattern, a predetermined number of the ceramic sheets having the conductive patterns are laminated to form a laminate, the laminate is fired, and thereafter, external electrodes are formed.
In the laminated ceramic electronic components, the thermal expansion coefficient of the conductive material used to form the internal electrode is different from the thermal expansion coefficient of the ceramic material. The shrinking behaviors of the two materials are different from each other. Therefore, a tensile stress is developed between the ceramic body and the internal electrode when the laminate is fired and cooled. This may cause structural defects in the laminate such as delamination. Moreover, if ferrite is used as the ceramic material, the impedance and the inductance are reduced, which may disadvantageously affect the electrical properties of the electronic component.
Thus, it is presumed that the tensile stress between the internal electrode and the ceramic body can be reduced by reduction of the contact ratio of the internal electrode with the ceramic body.
In Japanese Patent No. 2987176 (Patent Literature 1) the following solution is proposed. A plurality of spaces are arranged inside of a magnetic material layer which is the ceramic body. Conductor layers which are internal electrodes are embedded in the spaces in such a manner that gaps having a predetermined size remain. The average cross-sectional area ratio of the conductor layers present in the spaces is in the range of 10% to 85%. The contact ratio of the conductor layers with respect to the magnetic layers in the spaces is up to 50%, and the average area ratio of the voids in the conductor layers is in the range of 1% to 50%.
According to Patent Literature 1, a conductor layer is formed by using conductive paste. The conductive paste is formed by mixing such that the area ratio of the region not containing conductive particles on the outer surface of a formed film is in the range of 20% to 60%. Then, the conductor layer is fired. Thereby, the average cross-sectional area ratio of the conductor layers in the spaces is in the range of 10% to 85%, and thus, voids are intentionally formed between the magnetic layers and the conductor layers. In this way, influences on the magnetic layers caused by expansion or shrinkage of the conductor layers are reduced as much as possible, and the reduction of the electrical properties is prevented.
According to Patent Literature 1, the average cross-sectional area ratio is in the range of 10% to 85%. When the average cross-sectional area ratio is decreased, the amount of conductive particles in the conductor layers is reduced. Therefore, problematically, the DC resistance is increased, and disconnection easily occurs when a surge current is applied. Recently, great attention has been paid to such problems because the line widths of internal electrodes are becoming smaller with the decreasing sizes of electronic components.
Moreover, when the cross-sectional area ratio is decreased, the volume of the gaps is increased. Therefore, problematically, a plating liquid or a flux easily enters the gaps. Sulfur contained in the plating liquid or flux exerts a hazardous influence over the conductive particles. Thus, the reliability is deteriorated.